This invention relates generally to apparatus for transferring fluid between differentially rotating components, and more particularly, to rotating boundary fluid transfer seals for use in rotatable assemblies.
There are many applications which require that a fluid be controllably transferred across an interface between differentially rotatable components, i.e., in apparatus having at least one component which is rotatable with respect to at least one other adjacent component. Many of these applications involve fluid transfer between a stationary member to a rotating member. If the rotation is limited and cyclic such transfer can occur by use of flexible hoses which can wind and unwind as necessary. Alternatively, if the differential rotation is slow a rubbing transfer seal can be positioned firmly against the rotating surface to effectively maintain a sealing relationship, although wear and subsequent leakage are common problems with this type of arrangement. If, however, the rotational speed between the components is relatively high, friction will cause the rubbing transfer seals to quickly erode, rendering them generally ineffective and impractical for high speed applications.
One application which requires controllable fluid transfer between high speed differentially rotating components is in gas turbine engines of the type used in present day aircraft. For example, this may occur in a hydraulic system which extends through rotating engine components. By way of explanation, gas turbine engines generally include a gas generator which comprises a compressor for compressing air flowing aft through the engine, a combustor in which fuel is mixed with the compressed air and ignited to form a high energy gas stream, and a turbine driven by the gas stream and connected for driving a rotor which in turn drives the compressor. Many engines further include a second turbine, known as a power turbine, located aft of the gas generator and which extracts energy from the gas flow to drive a rotating load with variable pitch blades such as found in the propulsor of helicopters, ducted turbo fan engines, and turbo prop engines.
A recent improvement over the turbo-fan and turbo-prop engines is the unducted fan engine such as disclosed in U.S. patent application Ser. No. 71,594 filed July 10, 1987 which is a continuation of Ser. No. 728,466, filed May 1, 1985, now abandoned. In the unducted fan engine, the power turbine includes a pair of counter rotating rotors concentrically disposed about a stationary stator. Turbine blades associated with each rotor drive counter rotating unducted fan blades or propellers which extend radially outward from the rotors. In order to achieve optimum performance these propellers are hydraulically controllable variable pitch blades.
U.S. patent application Ser. No. 797,346 filed Nov. 12, 1985 entitled Propeller/Fan Pitch Feathering Apparatus, discloses a hydraulic actuating device locatable in each rotor of the unducted fan engine for varying the propeller blade pitch. To operate the device, hydraulic fluid must be transferred or pumped under pressure from a reservoir to a plurality of blade actuators which rotate with the rotor. Either an arrangement for transferring the fluid from a stationary reservoir to the rotor must be provided or the reservoir and associated pressurizing equipment must rotate with the rotor. However, rotation of the reservoir and equipment would substantially alter the inertial characteristics of the turbine in an undesirable manner.
It is an object of the present invention to provide a fluid transfer seal for transferring pressurized fluid between assemblies which are rotatable with respect to one another.
It is an object of the present invention to provide an apparatus for transferring fluid from a stationary member to a rotating member in a gas turbine engine.
It is another object of the present invention to provide a fluid transfer seal for transferring fluid between differentially rotating members with minimum seal wear.